This proposal describes a five-year training and career development program that will prepare its principle investigator, Dr. Vassilios Bezzerides, to be an independent investigator in the field of channelopathies and inherited arrhythmia disorders. This program will build on Dr. Bezzerides? existing background in cellular and clinical electrophysiology by providing additional expertise in induced pluripotent stem cells (iPSCs), genome editing, and translational research techniques. The principal mentor for this program will be Dr. William Pu, Professor of Pediatrics and Cardiology at Boston Children?s Hospital and Harvard Medical School. Dr. Pu is an internationally recognized expert in cardiac development and iPSC disease modeling. The enclosed proposal outlines a comprehensive training program with structured mentorship including an advisory committee with expertise in cardiovascular research and bioengineering, formal coursework, and a research plan that will provide rigorous training in disease modeling and novel therapy development. This proposal is focused on the investigation of novel therapeutic strategies for catecholaminergic polymorphic ventricular tachycardia (CPVT), a highly malignant inherited arrhythmia disorder characterized by life-threatening ventricular arrhythmias during times of stress or exercise. Current CPVT therapy is inadequate, with both therapy related toxicity and frequent treatment failures. Most CPVT cases are caused by mutations in ryanodine receptor type 2 (RYR2), which encodes the major cardiomyocyte intracellular Ca+2 release channel. Using iPSC-CMs, we developed a novel engineered human myocardial model (?opto-chip?) of CPVT that reproduces key features of this arrhythmia at a tissue level. Our preliminary data demonstrates that inhibition of Ca2+/calmodulin kinase II (CaMKII) blocks the pro-arrhythmic phenotype of CPVT iPSC-CMs. In Aim 1, using pharmacology, genome editing, and engineered tissues, Dr. Bezzerides will determine if CaMKII inhibition is a broadly applicable by evaluating pathogenic CPVT genotypes from each of the four canonical pathogenic regions within the RYR2 gene and determine the degree of inhibition necessary for arrhythmia suppression. In Aim 2, Dr. Bezzerides will further develop CaMKII inhibition as a clinically applicable therapeutic strategy for CPVT. To refine this strategy Dr. Bezzerides will test the effectiveness of target CaMKII in the cells of the cardiac conduction system using clinically relevant outcomes. A positive result would serve as the basis for further study as a step towards a first-in-human trial. In Aim 3, Dr. Bezzerides will use genome editing, patch clamp, and a second generation opto-chip assay to dissect the role of late sodium current blockade in the treatment of CPVT. Although controversial, late sodium current blockade may be the mechanistic basis for flecainide?s efficacy in CPVT. Better understanding of the mechanism may lead to new therapeutic options with greater efficacy and lower toxicity. Together, these studies will advance the understanding of arrhythmogenesis in CPVT, open new avenues for novel therapies, and provide a foundation for an independent research program led by Dr. Bezzerides.